Credit

Caption

Gravitational lensing. Pseudo-colour optical image of a possible "Einstein ring" associated with a cluster of galaxies known as Abell 963. The large red patch at centre is a giant galaxy which dominates the cluster. Surrounding it is the Einstein ring, seen here as two dark blue arcs; a longer one at bottom (south) and a shorter one at top. The arcs are thought to be the smeared-out image of a distant blue galaxy whose light has been "lensed" by the gravity of the Abell 963 cluster. Einstein proposed the effect of gravitational lensing in 1936. The image was made with the Isaac Newton Telescope on La Palma.